The leaders of three southern African nations signed a deal to proceed with a rail and port project to help land-locked Botswana export its massive coal reserves through a Mozambican port, though they still need to find the money to make it happen. The African Development Bank has agreed to finance a feasibility study for the project, at a cost of about $4-million, Mateus Magal, Mozambique’s transport and communications minister, said on Friday at the signing ceremony broadcast over state television.